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Hidden danger: Bumblebees can't taste lethal pesticides in nectar

A recent study conducted by the University of Oxford has uncovered a concerning insight into the world of bumblebees and their interaction with pesticides. 

Increased exposure

The researchers found that bumblebees are unable to taste pesticides in nectar, even when these pesticides are at levels that could be lethal. 

This finding is particularly alarming as it indicates that bumblebees cannot avoid ingesting contaminated nectar, thereby significantly increasing their risk of exposure to harmful pesticides.

Bumblebees and pesticides

“Bees are important pollinators of agricultural crops, but their populations are at risk when pesticides are used. One of the largest risks bees face is poisoning of floral nectar and pollen by insecticides,” wrote the researchers.

“Studies of bee detection of neonicotinoids have reported contradictory evidence about whether bees can taste these pesticides in sucrose solutions and hence avoid them.”

Detecting toxic compounds 

Given their innate ability to taste and differentiate between various sugary solutions, the team wanted to investigate if this sense of taste could extend to detecting and avoiding pesticides

Previous observations had shown that bumblebees could detect certain toxic compounds, such as quinine, which tastes bitter to them.

How the research was conducted 

The team, led by Dr. Rachel Parkinson of the University of Oxford’s Department of Biology, employed two distinct methods to assess the bumblebees’ ability to taste two types of pesticides: neonicotinoid and sulfoximine. 

The study focused on Bombus terrestris, a common species of bumblebee, and used nectar from oilseed rape (Brassica napus) as a base for the experiments. 

Bees’ response when tasting pesticides

The first method involved electrophysiology to record the neuron responses in the taste sensilla, akin to tastebuds, on the bumblebees’ mouthparts. 

This technique allowed the researchers to determine the strength of the bees’ response to the taste. The second method involved offering the bees sugar solutions with and without the addition of pesticides and observing their feeding behavior.

Critical insights into bees and pesticides

The results showed that there was no difference in neuron responses whether the bees consumed sugar solution alone or sugar solution mixed with pesticides. This indicates that the bumblebees’ mouthparts lack the mechanisms to detect common pesticides in nectar. 

Furthermore, in the behavioral tests, the bees consumed equal amounts of both the pesticide-laced and pesticide-free solutions, even when the pesticide concentration was high enough to be harmful.

Why this study is significant

“As bumblebees cannot taste pesticides and don’t experience immediate negative consequences from drinking them, they likely would not be able to avoid consuming nectar contaminated with pesticides in the field,” said Dr. Parkinson.

“This research is important when considering the use of pesticides on outdoor crops due to the risk posed to bees as they will not avoid drinking these compounds. Potentially, these findings could be applied towards searching for a non-toxic compound that tastes bad to bees and could be used as a ‘bee deterrent’ on pesticide-treated crops that do not require insect pollination.”

The researchers also explored the concept of “bitter” taste avoidance using quinine. While bees did not reduce their intake of the pesticide-infused solutions, they did show an aversion to quinine-laced sugar solutions at high concentrations, suggesting some ability to detect and react to specific bitter tastes.

Study implications 

The study highlights a critical issue in the interaction between bees and pesticides, with the inability of bees to taste and therefore avoid pesticide-contaminated nectar posing a significant threat to their health and their indispensable role in pollinating crops. 

The pesticides used in the study included neonicotinoids such as imidacloprid, thiamethoxam, clothianidin, and the sulfoximine pesticide sulfoxaflor. 

This research opens the door to future studies and potential strategies to mitigate the risks posed by pesticide use in agriculture, particularly in relation to bee health and pollination services.

The study is published in the journal eLife.

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